Polymerizable composition, cured object obtained therefrom, and composite material

ABSTRACT

There are provided a novel polymerizable composition having an X-ray contrast property and excellent transparency, a cured product thereof, and a composite material comprising powder of the cured product. More specifically, there are provided a polymerizable composition comprising (A) an inorganic oxide having an X-ray contrast property and an average particle diameter of 100 nm or smaller, (B) a surface modifier, (C) a polymerizable compound and (D) a polymerization initiator, a cured product obtained by polymerizing these components, and a composite material comprising powder of the cured product.

TECHNICAL FIELD

The present invention relates to a polymerizable composition whichcontains an inorganic oxide having an X-ray contrast property, a curedproduct thereof, and a composite material comprising powder of the curedproduct. More specifically, it relates to a polymerizable composition inwhich an inorganic oxide of 100 nm or smaller is dispersed uniformly andwhich has not only excellent transparency and surface gloss but also anX-ray contrast property and can be used not only for industrialmaterials but also for dental materials, a cured product thereof, and acomposite material comprising powder of the cured product.

BACKGROUND ART

In recent years, differences in various material properties have beenbecoming revealed, with a particle diameter of 100 nm as a boundary. Forexample, pigments are formed such that the particle diameters are atleast a half of the wavelength of visible light for the sake of highcoloring and concealing abilities. However, when the particle diametersare 100 nm or smaller, they do not show chromatic properties. Thus, thedevelopment of new toning has been expected. Meanwhile, magneticmaterials show a phenomenon that multiple magnetic domain particlesbecome single magnetic domain particles and magnetic properties changeat a boundary of around 100 nm. In expectation of such a novel property,studies have been made actively on ceramic materials, colored pigments,optical materials, electroconductive materials, piezoelectric materialsand the like. Meanwhile, as to the relationship between particlediameters of nano order (100 nm or smaller) and transparency,absorption, scattering and reflection must be low to improvetransparency. Further, it is known that when particle diameters areequal to or smaller than ¼ of the wavelength of visible light,scattering is low and transparency is high (refer to New Development ofNano Fine Particles, Toray Research Center, Inc., pp. 3 to 6).

In general, as exemplified by titanium white powders of fine particles,a transparent cured product is still obtained by adding inorganic oxideparticles powders having a refractive index different from that of apolymerizable compound by 0.1 or higher, an X-ray contrast property anda primary particle diameter of nano order in an amount of at least about3 parts by weight to 100 parts by weight of the polymerizable compound,adding a polymerization initiator and then fully kneading them topolymerize them. The reason is as follows. That is, since the surfaceenergy of primary particles becomes higher and the primary particlesbecome more unstable as the inorganic oxide particles become finer, theprimary particles are agglomerated firmly to lower the surface energy,thereby becoming stable. That is, when the particles are added to thepolymerizable compound, the size of the agglomerated particles isalready nearly equal to or larger than the wavelength of visible light,and it is extremely difficult to re-disperse most of the agglomeratedprimary particles, so that a transparent cured product cannot beobtained.

Meanwhile, (meth)acrylate-based materials are widely used not only asindustrial materials but also as dental materials due to theirproperties such as excellent transparency and good surface gloss.However, a (meth)acrylate alone shows a high polymerization shrinkageratio, and a cured product thereof shows poor mechanical strength andabrasion resistance. Thus, a number of studies have been made on acomposite of the (meth)acrylate and an inorganic oxide. JP-A 60-11505(the term “JP-A” as used herein means an “unexamined published Japanesepatent application”)-discloses a dental composition with improvedabrasion resistance which is obtained by adding a spherical inorganicoxide having a specific particle diameter to a vinyl compound and thenpolymerizing them. However, since the particle diameter of the inorganicoxide used in this method is 100 nm or larger, it is difficult to saythat the dental composition has excellent surface gloss, and theinorganic oxide may protrude or come off by abrasion, and the resultingabraded surface is a rough resin surface. Thus, when the composition isused for dental applications, it may cause such a problem as abrasion ofthe opposing tooth. Further, when a large quantity of an inorganic oxidehaving a particle diameter of 100 nm or smaller is added to apolymerizable compound, a significant increase in the viscosity of pasteoccurs due to the large specific surface area of the inorganic oxide andthe paste becomes unusable. On the other hand, when the quantity of theinorganic oxide is decreased, the paste becomes sticky and sticks to aspatula, so that in order to be practically used, it has a problem to besolved with respect to moldability. Meanwhile, JP-A 5-209027 disclosesthat a composite composition having excellent transparency and rigidityis obtained by uniformly dispersing silica in a vinyl compound by use ofcolloidal silica and a silane compound. According to this method, sincesilica of 100 nm or smaller can be dispersed uniformly, the compositionhas excellent transparency, and it is free of a problem of moldabilitycaused by an increase in viscosity. Further, JP-A 7-291817 discloses useof the above composite composition as a dental composition. However,since the composition uses colloidal silica, the inorganic oxide islimited to silica, and the obtained cured product has almost no X-raycontrast property. Therefore, when it is used as dental cement, a dentalfiller or the like, it can hardly be detected by an X-ray, so that it isdifficult to determine whether a treatment is successful and a problemmay occur. Further, the publication describes nothing about a method ofuniformly dispersing an inorganic oxide other than colloidal silica inthe polymerizable compound. In addition, when the composition is used inindustrial applications other than dental applications, hardness andabrasion resistance are improved; however, since silica is not capableof absorbing high-energy light having a shorter wavelength than that ofvisible light, e.g., ultraviolet light or a radiation, a cured productthereof may be degraded by yellowing or cracking when the cured productis exposed to outside.

DISCLOSURE OF THE INVENTION

The present inventors have paid attention to a colloidal solution inwhich fine particles having a primary particle diameter of 100 nm orsmaller are dispersed uniformly in a solvent without agglomeration, soas to obtain a polymerizable composition which is imparted with an X-raycontrast property without impairing excellent transparency, surfacegloss and moldability as of (meth)acrylate-based materials and a curedproduct thereof. That is, the present inventors have found that apolymerizable colloidal solution in which an inorganic oxide having anX-ray contrast property is dispersed in a polymerizable compound isobtained by using an aqueous colloidal solution in which the inorganicoxide having an X-ray contrast property is dispersed in water or anaqueous organic solvent as a starting material and replacing the solventby the polymerizable compound without agglomeration (gelation) ofcolloidal particles and that by further developing the polymerizablecolloidal solution, a novel polymerizable composition having an X-raycontrast property and excellent transparency, a cured product thereofand a composite material comprising powder of the cured product areobtained. The present inventors have achieved the present inventionbased on the finding.

According to the present invention, there are provided a polymerizablecomposition comprising (A) an inorganic oxide having an X-ray contrastproperty and an average particle diameter of 100 nm or smaller, (B) asurface modifier, (C) a polymerizable compound and (D) a polymerizationinitiator, a cured product obtained by polymerizing these components,and a composite material comprising powder of the cured product.

A characteristic of the present invention is that not only uniformdispersion of an inorganic oxide having a primary particle diameter ofan order of nanometer such as 100 nm or smaller in a polymerizablecompound which has been difficult to achieve but also impartation of anX-ray contrast property to a cured product obtained from thepolymerizable composition have become possible by use of a colloidalsolution in which an inorganic oxide having an X-ray contrast propertyis uniformly dispersed in water or an aqueous organic solvent, e.g., analcohol such as methanol or ethanol or acetone as a starting material.Another characteristic of the present invention is that since theinorganic oxide has an average particle diameter of 100 nm or smaller,there can be provided a polymerizable composition having better abrasionresistance and mechanical properties while retaining excellenttransparency and surface gloss as of (meth)acrylate-based materials, acured product thereof, and powder of the cured product. Further, thesecured product and powder also have an advantage that color matching ofdental filler, dental cement or the like is easily done due to theirexcellent transparency.

Hereinafter, the present invention will be further described. Thereby,the characteristics of the present invention will become more apparent.

As the inorganic oxide (A) having an X-ray contrast property and anaverage particle diameter of 100 nm or smaller and used in the presentinvention, a variety of commercial products and synthetic products canbe used. The inorganic oxide may be any inorganic oxide having an X-raycontrast property. Specific examples of the inorganic oxide includeinorganic oxides of aluminum, titanium, yttrium, zirconium, niobium,lanthanoid, antimony, barium, hafnium or strontium, inorganic oxidescontaining two or more elements at the same time such as bariumtitanate, and inorganic oxides resulting from mixing two or moreinorganic oxides. Of these, the elements of the groups 2A to 7Bexcluding silicon which constitutes silica are preferred, and inorganicoxides of titanium and zirconium are particularly preferably used due tosuch a reason that they are not so harmful to living bodies. Further,together with these inorganic oxides, silica having almost no X-raycontrast property can be used as long as the properties of the presentinvention are not impaired. Silica may also be contained and used in theinorganic oxide as a composite such as a silica/zirconia composite. Theaverage particle diameter of the inorganic oxide is generally 1 to 100nm. It is preferably 1 to 60 nm, more preferably 1 to 30 nm, in view oftransparency. The average particle diameter of the inorganic oxide isdetermined by a transmission electron microscope.

The inorganic oxide having an average particle diameter of 100 nm orsmaller and used in the present invention can be generally acquired asan aqueous colloidal solution of water, an aqueous organic solvent or amixed solvent of water and an aqueous organic solvent. As the solvent ofthe aqueous colloidal solution of the inorganic oxide, an aqueousorganic solvent, e.g., an alcohol having 1 to 5 carbon atoms such asmethanol, ethanol and isopropyl alcohol, cellosolves and dimethylacetamide, water or the like is used. Preferably, an alcohol which canbe uniformly mixed with water, cellosolve and water are used alone or inadmixture. Further, as long as colloidal particles are not agglomerated,the aqueous organic solvent and water may be mixed together in a givenratio and used. Although the pH of the solution of the inorganic oxide(A) is not particularly limited, the solution is preferably neutral oracidic to use the following surface modifier (B), and the pH isparticularly preferably 3 to 7.

In the aqueous colloidal solution of the inorganic oxide (A), a colloidstabilizer (E) is generally contained in an amount of 0.1 to 70 wt %based on 100 parts by weight of (A). Illustrative examples of thecolloid stabilizer (E) include acidic compounds such as hydrochloricacid, nitric acid, oxalic acid and acetic acid and alkaline compoundssuch as ammonia.

The surface modifier (B) used in the present invention may be anysurface modifier which can modify the surface of the inorganic oxide(A). An alkoxysilane compound is preferably used. In particular, analkoxysilane compound represented by the following formula (I):SiR¹ _(a)R² _(b)(OR³)_(c)  (I)wherein R¹ and R² each independently represent a substituent with 1 to20 carbon atoms which may have an ether bond, an ester bond, an epoxybond or a carbon-carbon double bond and which may also have a nitrogenatom, a sulfur atom or a phosphorus atom, R³ represents a hydrogen atomor a substituent with 1 to 20 carbon atoms which may have an ether bond,an ester bond or a carbon-carbon double bond and which may also have anitrogen atom, a sulfur atom or a phosphorus atom, a and b represent aninteger of 0 to 3, and c satisfies c=4−a−b and represents an integer of1 to 4, is preferably used. Alkoxysilane compounds represented by thefollowing formulae (I-A) to (I-F):SiR⁴ _(a)R⁵ _(b)(OR⁶)_(c)  (I-A)SiR⁴ _(d)(O—CH₂CH₂—OCO—(R⁷)C═CH₂)_(4-d)  (I-B)CH₂═C(R⁷)COO(CH₂)_(e)SiR⁸ _(d)(OR⁶)_(3-d)  (I-C)CH₂═CSiR⁸ _(d)(OR⁶)_(3-d)  (I-D)HS(CH₂)_(e)—SiR⁸ _(d)(OR⁶)_(3-d)  (I-E)CH₂═C(R⁷)—C₆H₄—SiR⁸ _(d)(OR⁶)_(3-d)  (I-F)wherein R⁴ and R⁵ each independently represent a substituent with 1 to20 carbon atoms which may have an ether bond, an ester bond, an epoxybond or a carbon-carbon double bond and which may also have a nitrogenatom, a sulfur atom or a phosphorus atom, R⁶ represents a hydrogen atomor a hydrocarbon residue having 1 to 20 carbon atoms, R⁷ represents ahydrogen atom or a methyl group, R⁸ represents an alkyl group having 1to 3 carbon atoms or a phenyl group, a and b represent an integer of 0to 3, c satisfies c=4−a−b and represents an integer of 1 to 4, drepresents an integer of 0 to 2, and e represents an integer of 1 to 6,are particularly preferably used.

Illustrative examples of the silane compound represented by the aboveformula (I-A) include tetramethoxysilane, tetraethoxysilane,tetrapropoxysilane, tetrabutoxysilane, methyl triethoxysilane, ethyltrimethoxysilane, ethyl triethoxysilane, phenyl trimethoxysilane, phenyltriethoxysilane, dimethyl dimethoxysilane, diphenyl dimethoxysilane,methylethyl diethoxysilane, methylphenyl dimethoxysilane,trimethylmethoxysilane, trimethylethoxysilane, methoxyethyltriethoxysilane, trimethoxyhexylsilane, trimethoxyoctylsilane,acetoxyethyl triethoxysilane, tetraacetoxysilane, methyltriacetoxysilane, tetrakis(2-methoxyethoxy)silane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyl triethoxysilane,γ-glycidoxypropylmethyl dimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, β-(3,4-epoxycyclohexyl)ethyl trimethoxysilane andβ-(3,4-epoxycyclohexyl)ethyl triethoxysilane.

Illustrative examples of the silane compound represented by the aboveformula (I-B) include tetrakis(acryloxyethoxy)silane,tetrakis(methacryloxyethoxy)silane and methyltris(methacryloxyethoxy)silane.

Illustrative examples of the silane compound represented by the aboveformula (I-C) include β-(meth)acryloxyethyl dimethoxymethylsilane,γ-(meth)acryloxypropyl methoxydimethylsilane, γ-(meth)acryloxypropyltrimethoxysilane, β-(meth)acryloxyethyl diethoxymethylsilane,γ-(meth)acryloxypropyl ethoxydimethylsilane, γ-(meth)acryloxypropyldimethylethoxysilane, γ-(meth)acryloxypropyl methyldiethoxysilane, andγ-(meth)acryloxypropyl triethyloxysilane.

Illustrative examples of the silane compound represented by the aboveformula (I-D) include vinyl methyl dimethoxysilane, vinyltrimethoxysilane and vinyl triethoxysilane.

Illustrative examples of the silane compound represented by the aboveformula (I-E) include γ-mercaptopropyl dimethoxymethylsilane andγ-mercaptopropyl trimethoxysilane.

Illustrative examples of the silane compound represented by the aboveformula (I-F) include p-vinyl phenylmethyl dimethoxysilane and p-vinylphenyl trimethoxysilane.

As compounds containing hetero atoms, generally used silane couplingagents such as N-β(N-vinylbenzylaminoethyl)-γ-aminopropyltrimethoxysilane hydrochloride, γ-mercaptopropyl trimethoxysilane andoctadecyl dimethyl[3-(trimethoxysilyl)propyl]ammonium chloride can alsobe used without limitations.

Of the compounds represented by the above formula (I),γ-(meth)acryloxypropyl dimethyl methoxysilane, γ-(meth)acryloxypropylmethyl dimethoxysilane, γ-(meth)acryloxypropyl trimethoxysilane,γ-(meth)acryloxypropyl dimethyl ethoxysilane, γ-(meth)acryloxypropylmethyl diethoxysilane and γ-(meth)acryloxypropyl triethoxysilane areparticularly preferably used.

Further, titanium-based, zirconia-based, aluminum-based andzircoaluminate-based surface modifiers different from the above surfacemodifiers can also be used without any problems. Further, the silanecoupling agents represented by the above formula (I) and the surfacemodifiers other than these silane coupling agents can be used togetherwithout any problems as long as the properties of the composite materialof the present invention are not impaired.

Next, the amount of the surface modifier (B) to be added to the aqueouscolloidal solution containing the inorganic oxide (A) and a method ofadding the surface modifier (B) to the aqueous colloidal solution willbe described. When the amount of the surface modifier (B) is too small,the inorganic oxide is not dispersed uniformly when the solvent isreplaced by the polymerizable compound, so that a polymerizablecomposition having excellent transparency and a cured product thereofmay not be obtained disadvantageously. Accordingly, the preferred amountof the surface modifier (B) is preferably 10 to 500 parts by weight,more preferably 10 to 350 parts by weight, particularly preferably 10 to250 parts by weight, based on 100 parts by weight of the inorganic oxide(A). When a hydrolyzed or partially hydrolyzed compound or a compoundresulting from condensation of two or more molecules is to be added, itis preferably added in the above amount. Further, when the abovealkoxysilane compound is used as the surface modifier (B), a method ofadding the alkoxysilane compound is not particularly limited, and amethod of directly adding a solution of the alkoxysilane compound as thesurface modifier (B) in an aqueous organic solvent to the aqueouscolloidal solution containing the inorganic oxide (A) or a method ofadding a hydrolysate of the surface modifier (B) can be used. When ahydrolysate of the surface modifier (B) is to be added, there can beemployed a method using a solution prepared by adding water or a uniformsolution of alcohol and acidic water in an amount of at least 0.5 molesper mole of the alkoxysilane compound and then treating the mixture atroom temperature to a reflux temperature for several minutes to severaltens of hours.

The solid concentration of the aqueous colloidal solution containing theinorganic oxide (A) is preferably 1 to 50 wt %, more preferably 1 to 30wt %. When the solid concentration is lower than 1 wt %, the solution isso dilute that when the organic solvent or water which is a dispersionmedium of the colloidal solution is replaced by the polymerizablecompound, the amount removed of the solvent becomes large or the amountadded of the polymerizable compound (C) becomes so low that a decreasein the productivity of the polymerizable composition may occur.Meanwhile, when the solid concentration is higher than 50 wt %, thecolloidal solution becomes unstable and is liable to geldisadvantageously.

In one example of preferable methods for preparing the polymerizablecomposition, the aqueous colloidal solution of the inorganic oxide isprepared, with or without being mixed with an aqueous solvent which doesnot cause the colloidal solution to gel such as methanol, ethanol orisopropyl alcohol, such that the solid concentration of the colloidalsolution becomes 1 to 30 wt %. After the alkoxysilane compound is addedto this solution, the resulting solution is stirred at room temperatureto a reflux temperature for several minutes to several tens of hours,and the polymerizable compound is then added. Alternatively, it is alsopossible that the alkoxysilane compound and the aqueous solvent such asmethanol are mixed uniformly first and the aqueous colloidal solution ofthe inorganic oxide is added thereto and stirred to achieve a desiredsolid concentration. Alternatively, a compound resulting fromhydrolyzation or partial hydrolyzation of the alkoxysilane compound orcondensation of two or more molecules of the compound may be added tothe colloidal solution and stirred as described above. As long as thetransparency of the colloidal solution is not degraded and gelation ofthe colloidal solution is not induced, the polymerizable compound toreplace the solvent may be added to the colloidal solution immediatelyafter addition of the alkoxysilane compound or the alkoxysilane compoundand the polymerizable compound may be added simultaneously and stirred.Further, when the colloidal solution containing the inorganic oxide (A)is not an acidic solution, an acidic compound may be added to thecolloidal solution in order to adjust the rate of hydrolysis of thealkoxysilane compound and promote the affinity of the alkoxysilanecompound for the inorganic oxide, as long as colloidal particles do notgel. As the acidic compound, an inorganic acid or an organic acid can beused. Illustrative examples of the inorganic acid include halogenatedhydroacids such as hydrogen fluoride, hydrogen bromide and hydrochloricacid, and mineral acids such as nitric acid, sulfuric acid andphosphoric acid. Illustrative examples of the organic acid includeformic acid, acetic acid, oxalic acid, acrylic acid and methacrylicacid. Of these, hydrochloric acid and acetic acid can be preferablyused. Further, the colloidal solution containing the inorganic oxide (A)is preferably not an alkaline solution because the silane coupling agentmay gel alone.

A method of replacing the alcohol or water which is a dispersion mediumof the colloidal solution containing the above alkoxysilane compoundwith the polymerizable compound is not particularly limited, and a knownmethod can be used. For example, it is possible that after a givenamount of the polymerizable compound is added directly to the colloidalsolution and stirred until the solution becomes uniform, the solution isheated at normal pressure or heated under reduced pressure by a rotaryevaporator or the like to remove the alcohol or water, or thepolymerizable compound is gradually added as the alcohol or water isremoved by reflux at normal pressure. To be more specific about themethod of removing the dispersion medium and the amount removed of thedispersion medium, it is not removed all at once by a rotary evaporatoror the like, but it is preferable that about 60 parts by weight (about60 wt % of the solvent) based on 100 parts by weight of the solvent tobe removed be removed first, about 60 parts by weight of solventazeotropic with water such as isopropyl alcohol be then added, and thesolution be heated again under reduced pressure to remove the solvent.Thereby, the inorganic oxide can be dispersed uniformly in thepolymerizable compound, and the target polymerizable composition isobtained. In the polymerizable composition, the colloid stabilizer (E)is preferably contained in an amount of 0.1 to 150 parts by weight, morepreferably 0.1 to 100 parts by weight, particularly preferably 0.1 to 80parts by weight, based on 100 parts by weight of (A). To remove anacidic compound such as the colloid stabilizer (E) and impurities suchas halogen from the polymerizable composition, a known method can beused. For example, the polymerizable composition may be rinsed withwater or an alkaline solution, an acidic compound absorbent (such asKYOWORD of Kyowa Chemical Industry Co., Ltd.) comprising molecularsieves, zeolite, Al, Mg, Si or the like may be added to absorb or adsorbthe acidic compound, the acidic compound may be removed from thepolymerizable composition or a solution obtained by diluting thepolymerizable composition with an organic solvent by a dialysis membraneor an ultrafiltration method, or a cured product obtained bypolymerizing the polymerizable composition or powder obtained by millingthe cured product may be rinsed with a solvent such as water or anaqueous organic solvent in which the acidic compound is soluble or maybe neutralized with an alkaline aqueous solution to remove the acidiccompound. Further, the acidic compound may be removed by use of zeolite,molecular sieves, an acidic compound absorbent, a dialysis membrane oran ultrafiltration membrane in accordance with an ordinary method. Whena cured product obtained by polymerizing the polymerizable compositionor powder of the cured product is used in a composite material, thecolloid stabilizer (E) is preferably removed completely.

The type of the polymerizable compound (C) used in the present inventionis not particularly limited, and a variety of conventionally knownpolymerizable compounds can be used. Preferably, the followingpolymerizable monofunctional, bifunctional and polyfunctional(meth)acrylates, urethane compounds and polyester di(meth)acrylatecompounds can be used and are selected as appropriate according toapplication purposes. Examples of the polymerizable compounds are asfollows.

(i) Monofunctional Polymerizable Compounds

Illustrative examples of monofunctional polymerizable compounds include(meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate,propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate,pentyl (meth)acrylate, isopentyl (meth)acrylate, glycidyl(meth)acrylate, tetrafurfuryl (meth)acrylate, 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-chloro-2-hydroxypropyl(meth)acrylate, ethylene glycol mono(meth)acrylate, diethylene glycolmono(meth)acrylate, triethylene glycol mono(meth)acrylate, polyethyleneglycol mono(meth)acrylate, methoxy diethylene glycol mono(meth)acrylate,methoxy tetraethylene glycol (meth)acrylate, methoxy polyethylene glycol(meth)acrylate, β-(meth)acryloxyethyl hydrogen phthalate,β-(meth)acryloxyethyl hydrogen succinate, nonylphenoxyethyl(meth)acrylate, phenoxyethyl (meth)acrylate, phenoxy diethylene(meth)acrylate, N-(2-hydroxy-3-(meth)acryloyloxypropyl)-N-phenylglycine, N-(meth)acryloyl glycine and 4-(meth)acryloyloxyethyltrimellitic anhydride; vinyl esters such as vinyl acetate and vinylpropionate; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether,isobutyl vinyl ether and (meth)acryl aldehyde ethyl acetal; alkenylbenzenes such as styrene, vinyl toluene, α-methyl styrene andchlorostyrene; vinyl cyanides such as acrylonitrile andmethacrylonitrile; (meth)acryl aldehydes such as (meth) acryl aldehydeand 3-cyano (meth) acryl aldehyde; (meth)acrylic amides such as(meth)acrylamide, N-succin(meth)acrylamide and N,N-dimethyl(meth)acrylamide; (meth)acrylic acids such as (meth)acrylic acid, vinylacetic acid and crotonic acid or metal salts thereof;phosphate-group-containing polymerizable compounds such as acidphosphoethyl (meth)acrylate, acid phosphopropyl (meth)acrylate and2-(meth)acryloyloxyethylphenyl phosphoric acid or metal salts thereof;and sulfonic-group-containing polymerizable compounds such as allylsulfonic acid, methallyl sulfonic acid, styrene sulfonic acid andt-butyl acrylamide sulfonic acid or metal salts thereof. Methylmethacrylate and ethyl methacrylate are particularly preferred.

(ii) Bifunctional Polymerizable Compounds

The bifunctional polymerizable compound is a compound represented by thefollowing general formula (II):

wherein f is an integer of 1 to 30, and R⁹ and R¹⁰ each independentlyrepresent H or an alkyl group having 1 to 5 carbon atoms. Illustrativeexamples of the compound include di(meth)acrylates such as propanediol,butanediol, hexanediol, octanediol, nonanediol, decanediol andeicosanediol; ethylene glycol di(meth)acrylate, diethylene glycoldi(meth)acrylate, triethylene glycol di(meth)acrylate, propylene glycoldi(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethyleneglycol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, neopentylglycol di(meth)acrylate; urethane-based polymerizable compounds derivedfrom adducts of hydroxyl-group-containing vinyl compounds such as2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate and3-chloro-2-hydroxypropyl (meth)acrylate and diisocyanate compounds suchas hexamethylene diisocyanate, trimethylhexamethylene diisocyanate,diisocyanate methylcyclohexane, isophorone diisocyanate and methylbis(4-cyclohexylisocyanate); (meth)acrylate-based polymerizablecompounds having an aromatic ring and an urethane bond and derived fromadducts of hydroxyl-group-containing vinyl compounds such as2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate and3-chloro-2-hydroxypropyl (meth)acrylate and aromatic-containingdiisocyanate compounds such as diisocyanate methylbenzene and4,4′-diphenylmethane diisocyanate; and (meth)acrylate-basedpolymerizable compounds having an aromatic ring and an ether bond suchas 2,2-bis((meth)acryloxyphenyl)propane,2,2-bis[4-(3-(meth)acryloxy)-2-hydroxypropoxyphenyl]propane,2,2-bis(4-(meth)acryloxyethoxyphenyl)propane,2,2-bis(4-(meth)acryloxydiethoxyphenyl)propane,2,2-bis(4-(meth)acryloxytetraethoxyphenyl)propane,2,2-bis(4-(meth)acryloxypentaethoxyphenyl)propane,2,2-bis(4-(meth)acryloxypolyethoxyphenyl)propane,2,2-bis(4-(meth)acryloxydipropoxyphenyl)propane,2(4-(meth)acryloxyethoxyphenyl)-2(4-(meth)acryloxyphenyl) propane,2(4-(meth)acryloxydiethoxyphenyl)-2(4-(meth)acryloxytriethoxyphenyl)propane,2(4-(meth)acryloxydiethoxyphenyl)-2(4-(meth)acryloxytriethoxyphenyl)propane,2(4-(meth)acryloxydipropoxyphenyl)-2(4-(meth)acryloxytriethoxyphenyl)propane, and2,2-bis(4-(meth)acryloxyisopropoxyphenyl)propane. Of these, triethyleneglycol dimethacrylate and di (methacryloxy ethyl)trimethylhexamethylenediurethane are particularly preferably used.(iii) Polymerizable Compounds Having Three or More Functional Groups

A (meth)acrylate compound having three or more ethylenic unsaturatedgroups in a molecule may be a compound represented by the followingformula (III):

wherein R¹¹, R¹² and R¹³ are each independently a group represented bythe following formula:

(wherein g is 1 to 10, h is 0 to 2, and R¹⁵ is H or an alkyl grouphaving 1 to 5 carbon atoms),and R¹⁴ is H, an alkyl group having 1 to 5 carbon atoms or ahydroxyalkyl group having 1 to 5 carbon atoms, orR¹¹, R¹², R¹³ and R¹⁴ are each independently a group represented by thefollowing formula:

(wherein g is 1 to 10, h is 0 to 2, and R¹⁵ is H or an alkyl grouphaving 1 to 5 carbon atoms.)

Two or more compounds represented by the formula (III) may be usedtogether.

Illustrative examples of the compound represented by the formula (III)include trimethylolmethane tri(meth)acrylate, trimethylolethanetri(meth)acrylate, trimethylolpropane tri(meth)acrylate,trimethylolbutane tri(meth)acrylate, tri(methyleneoxyl)methylolmethanetri(meth)acrylate, tri(ethyleneoxyl)methylolmethane tri(meth)acrylate,tri(propyleneoxyl)methylolmethane tri(meth)acrylate,tri(diethyleneoxyl)methylolmethane tri(meth)acrylate,tri(dipropyleneoxyl)methylolmethane tri(meth)acrylate, pentaerythritoltri(meth)acrylate, and pentaerythritol tetra(meth)acrylate. Of these,trimethylolpropane tri(meth)acrylate is preferably used.

Further, the (meth)acrylate compound having three or more ethylenicunsaturated groups in a molecule may be a compound represented by thefollowing formula (IV):

wherein R¹⁶, R¹⁷, R¹⁸, R¹⁹, R²⁰ and R²¹ are each independently a grouprepresented by the following formula:

(wherein i is 1 to 10, j is 0 to 2, and R²² is H or an alkyl grouphaving 1 to 5 carbon atoms), orR¹⁶, R¹⁷, R²⁰ and R²¹ are each independently a group represented by thefollowing formula:

(wherein i is 1 to 10, j is 0 to 2, and R²² is H or an alkyl grouphaving 1 to 5 carbon atoms),and R¹⁸ and R¹⁹ each independently represent H, an alkyl group having 1to 5 carbon atoms or a hydroxyalkyl group having 1 to 5 carbon atoms.

Illustrative examples of the compound represented by the formula (IV)include dipentaerythritol penta(meth)acrylate, pentaerythritolhexa(meth)acrylate, dipentaerythritol hexa(meth)acrylate, andditrimethylolpropane tetra(meth)acrylate. Of these, dipentaerythritolhexa(meth)acrylate and ditrimethylolpropane tetra(meth)acrylate arepreferably used, and ditrimethylolpropane tetra(meth)acrylate is morepreferred.

Further, illustrative examples of a polyester di(meth)acrylate compoundhaving an ethylenic unsaturated group in a molecule include a compoundrepresented by the following formula (V):

(wherein k, k′, m and m′ are 1 to 10, 1 and n are 0 to 7 and satisfy1+n≧1, R²³ and R²⁸ are each independently H or an alkyl group having 1to 5 carbon atoms, and R²⁴, R²⁵, R²⁶ and R²⁷ each independentlyrepresent H or an alkyl group having 1 to 5 carbon atoms),a compound represented by the following formula (VI):

(wherein o is 1 to 10, p is 0 to 7, q is 1 to 10, R²⁹ and R³⁰ are eachindependently H or an alkyl group having 1 to 5 carbon atoms),and a compound represented by the following formula (VII):

(wherein Y is a group represented by —(CH₂)_(n)—, —CH₂CH(CH₃)—,—CH₂C(CH₃)₂CH₂—, —CH₂C₆H₁₀CH₂—, —CH₂CH₂(OCH₂CH₂)_(t)—,

s is 2 to 6, t is 1 to 15, u is 1 to 10, v is 1 to 5, R³¹ and R³² areeach independently H or an alkyl group having 1 to 5 carbon atoms, Z isa group represented by —CH₂CH₂—,

and r is an integer of 1 to 3.)

The above polyester di(meth)acrylates have a plurality of ester bondsand (meth)acryloyl groups in a molecule and generally include allcompounds obtained by a reaction between a polybasic acid anhydride anda (meth)acrylate having a hydroxyl group or a dehydration reaction inbetween a polybasic acid, a polyhydric alcohol and (meth)acrylic acid.

Two or more of the compounds represented by the above formulae (V), (VI)and (VII) may be used together. Further, a polyester di(meth)acrylaterepresented by the above formula (V) in which k=m=5 and 1+n=2 or k=m=5and 1+n=4 is preferably used, and a polyester di(meth)acrylaterepresented by the following formula (VIII) which is the above formula(V) in which k=m=5, k′=m′=1 and 1+n=2 or k=m=5, k′=m′ =1 and 1+n=4 andR²⁴, R²⁵, R²⁶ and R²⁷ are CH₃ is more preferably used.

Polymerizable compounds having two or more functional groups includecompounds having a methacrylate group and an acrylate group in amolecule, such as triethylene glycol acrylate methacrylate,trimethylolpropane monoacrylate dimethacrylate and pentaerythtitoldiacrylate dimethacrylate.

A monofunctional compound is preferably mixed with a polymerizablecompound having two or more functional groups before use becausestrength and the like may deteriorate when the monofunctional compoundis used alone. The content of the polymerizable compound (C) in thepolymerizable composition of the present invention is preferably 10 to1,000 parts by weight, more preferably 10 to 800 parts by weight,particularly preferably 10 to 600 parts by weight, based on 100 parts byweight of the inorganic oxide (A), from the viewpoints of an X-raycontrast property and operability to be imparted.

As the polymerization initiator (D) used in the present invention, knownpolymerization initiators such as a heat polymerization orphotopolymerization initiator and a redox-based initiator can be usedwithout limitations. As the heat polymerization initiator, an organicperoxide, a diazo-based compound or the like can be preferably used.When it is desired that polymerization be carried out efficiently in ashort time, a compound whose decomposition half life at 80° C. is 10hours or less is preferred. Illustrative examples of the organicperoxide include diacyl peroxides such as acetyl peroxide, isobutylperoxide, decanoyl peroxide, benzoyl peroxide and succinic peroxide;peroxydicarbonates such as diisopropyl peroxydicarbonate,di-2-ethylhexyl peroxydicarbonate and diallyl peroxydicarbonate;peroxyesters such as t-butyl peroxyisobutyrate, t-butyl neodecanate andcumene peroxyneodecanate; and sulfonyl peroxides such as acetylcyclohexyl sulfonyl peroxide. Illustrative examples of the diazo-basedcompounds include 2,2′-azobisisobutylonitrile,4,4′-azobis(4-cyanovaleric acid),2,2′-azobis(4-methoxy-2,4-dimethoxyvaleronitrile) and2,2′-azobis(2-cyclopropylpropionitrile). Benzoyl peroxide and2,2′-azobisisobutylonitrile are particularly preferred. Further, as theredox initiator, a reducing agent such as an amine can be used togetherwith the heat polymerization initiator. Further, as thephotopolymerization initiator, a photosensitizer or a combination of aphotosensitizer and a photopolymerization accelerator can be used.Illustrative examples of the photosensitizer include known compoundswhich are excited and initiate polymerization by irradiation of visiblelight or ultraviolet light, such as benzyl, an α-diketone compound,camphorquinone, α-naphthyl, p,p′-dimethoxybenzyl, pentadione,1,4-phenanthrenequinone, naphthoquinone, and an acyl phosphine oxidederivative such as diphenyl trimethyl benzoyl phosphine oxide. These maybe used alone or in combination of two or more. Camphorquinone anddiphenyl trimethyl benzoyl phosphine oxide are particularly preferablyused.

Illustrative examples of the photopolymerization accelerator includeorganic peroxides such as benzoyl oxide, acyl phosphine oxides orderivatives thereof, tertiary amines such as N,N-dimethyl aniline,N,N-diethyl aniline, N,N-dibenzyl aniline, N,N-dimethyl-p-toluidine,p-N,N-dimethylaminobenzoic acid, p-N,N-diethylaminobenzoic acid, ethylp-N,N-dimethylaminobenzoate, ethyl p-N,N-diethylaminobenzoate, methylp-N,N-dimethylaminobenzoate, methyl p-N,N-diethylaminobenzoate,p-N,N-dimethylaminobenzaldehyde, 2-n-butoxyethylp-N,N-dimethylaminobenzoate, 2-n-butoxyethyl p-N,N-diethylaminobenzoate,p-N,N-dimethylaminobenzonitrile, p-N,N-diethylaminobenzonitrile,p-N,N-dihydroxyethyl aniline, p-dimethylaminophenethyl alcohol,N,N-dimethylaminoethyl methacrylate, triethylamine, tributylamine,tripropylamine and N-ethyl ethanolamine, combinations of citric acid,malic acid or 2-hydroxypropanoic acid and the above tertiary amines,barbituric acids such as 5-butylaminobarbituric acid and1-benzyl-5-phenyl barbituric acid, and organic peroxides such as benzoylperoxide and di-t-butyl peroxide. They may be used alone or in admixtureof two or more. Tertiary aromatic amines in which a nitrogen atom isdirectly bonded to an aromatic or aliphatic tertiary amines having apolymerizable group, such as ethyl p-N,N-dimethylaminobenzoate,2-n-butoxyethyl p-N,N-dimethylaminobenzoate and N,N-dimethylaminoethylmethacrylate, acyl phosphine oxides or derivatives thereof areparticularly preferably used. To end curing quickly, a combination of aphotosensitizer and a photopolymerization accelerator is preferred. Forexample, a combination of camphorquinone and a tertiary aromatic amineester compound in which a nitrogen atom is directly bonded to anaromatic, such as ethyl p-N,N-dimethylaminobenzoate or 2-n-butoxyethylp-N,N-dimethylaminobenzoate or an acyl phosphine oxide is preferablyused. The photopolymerization accelerator is preferably used in anamount of 1 to 100 parts by weight, based on 100 parts by weight of thepolymerization initiator. The amount of the polymerization initiator (D)in the present invention is preferably 0.01 to 5 parts by weight, morepreferably 0.01 to 1 part by weight, based on 100 parts by weight of thetotal of the components (A), (B) and (C).

As for addition of the polymerization initiator to the polymerizablecomposition, it may be added by use of a kneader after preparation of apolymerizable colloidal solution, or a solution obtained by dissolvingthe polymerization initiator in an organic solvent may be added to anddispersed in the polymerizable colloidal solution during the preparationstep of the polymerizable colloidal solution as long as agglomeration ofinorganic oxides does not occur and the transparency of the colloidalsolution is not affected.

A polymerization method for obtaining a cured product of thepolymerizable composition is not particularly limited, and a knownpolymerization method can be employed. Further, to obtain powder (F) ofthe cured product of the polymerizable composition, a method comprisingcharging the polymerizable composition into a mold and heat-setting thecomposition by a heating compression molding machine under a pressure of0.1 to 20 MPa at 60 to 200° C. for several minutes to several hours canbe preferably used since it facilitates the operation of polymerization.This cured product is then milled by use of a dry mill such as a ballmill or a jet mill or a wet mill such as an apex mill, thereby givingthe powder. If necessary, the powder may be classified to desiredparticle diameters by a sieve or the like before use. The averageparticle diameter of the powder of the cured product is preferably 1 to100 μm, more preferably 1 to 50 μm, particularly preferably 1 to 35 μm.Further, a peroxide is produced during milling of the cured product, andwhen the resulting powder including the peroxide is added to thepolymerizable compound as it is, the storage stability of paste maybecome significantly poor. Thus, the powder is preferably used aftertreated with a sodium sulfite aqueous solution, rinsed with water anddried or after heat-treated in a nitrogen atmosphere under an aircurrent at 60 to 180° C., preferably 80 to 150° C., for several minutesto several tens of hours, preferably several hours to several tens ofhours, so as to reduce the produced peroxide.

Thus, the cured product is obtained by polymerizing the polymerizablecomposition containing the polymerization initiator. To improve thestability of the polymerizable composition, a known polymerizationinhibitor such as hydroquinone, 4-methoxyphenol, 2,6-di-t-butyl-p-cresolor hindered amine may be added. The amount of the polymerizationinhibitor is not particularly limited but preferably ranges from 50 to5,000 ppm based on the polymerizable compound.

As for the transparency of the cured product of the polymerizablecomposition, the cured product should have transparency of such a degreethat does not affect the toning of an application in which it is used.In general, when the thickness of the cured product is 2.0 mm, the curedproduct preferably shows a light transmittance at a visible lightwavelength of 560 nm of 1% or higher, more preferably 2% or higher.

Further, as in the case of the above transparency, the X-ray contrastproperty of the cured product of the polymerizable composition can bedetermined according to an application in which it is used. Based on thesensitivity of an X-ray which is generally used in dentistry (measuredin accordance with the X-ray contrast property test of 5.11 of JIST6514-1993), the cured product generally shows an Al equivalent of 45%or higher, preferably 55 to 400%, more preferably 80 to 300% or higher,when the thickness of the cured product is 2.0 mm.

Next, a composite material for dental use and industrial use will bedescribed. As for the transparency of a cured product of a compositematerial obtained by adding the powder of the cured product of the abovepolymerizable composition to the polymerizable compound, the curedproduct should have transparency of such a degree that does not affectthe toning of an application in which it is used, as in the case of thecured product of the polymerizable composition. In general, when thethickness of the cured product of the composite material is 2.0 mm, thecured product preferably shows a light transmittance at a visible lightwavelength of 560 nm of 1% or higher, more preferably 2% or higher.

The amount of the powder of the cured product of the polymerizablecomposition in the composite material is determined according to arequired X-ray contrast property, viscosity, operability and the likeand is preferably 1 to 80 parts by weight, more preferably 5 to 70 partsby weight, based on 100 parts by weight of the polymerizable compound inthe composite material.

The powder of the cured product of the polymerizable composition of thepresent invention is added to the composite material for dental use soas to impart the operability of the composite material, the X-raycontrast property and transparency of the cured product of the compositematerial, gloss after polishing, and ease of removal of an excess curedproduct when used as an adhesive resin cement.

As the polymerizable compound in the composite material, thepolymerizable compound (C) used in the above polymerizable compositionis used.

In consideration of the operability of the composite material and thephysical properties of the cured product thereof, an inorganic filler ispreferably also added to the composite material. The shape of theinorganic filler may be spherical or amorphous and is selected asappropriate together with the particle diameter. As for the type of theinorganic filler, there can be used known inorganic fillers such as thegroups I, II, III and IV and transition metals of the periodic table andoxides, hydroxides, chlorides, sulfates, sulfites, carbonates,phosphates and silicates thereof, and mixtures and composite saltsthereof. More specifically, the inorganic fillers include glass powderssuch as silicon dioxide, strontium glass, lanthanum glass and bariumglass, quartz powder, barium sulfate, aluminum oxide, titanium oxide,barium salts, glass beads, glass fibers, bariumfluoride, lead salts,talc-containing glass powder, colloidal silica, silica gel, zirconiumoxide, tin oxide, carbon fibers, and other ceramic powders. Although theinorganic filler may be used as it is, it is preferably renderedhydrophobic for the purpose of, for example, increasing the amount ofthe inorganic filler by increasing affinity between the polymerizablecompound and the inorganic filler by use of a surface modifier. As thesurface modifier, those described above can be used without limitations,and γ-(meth)acryloxypropyl dimethyl methoxysilane,γ-(meth)acryloxypropyl methyl dimethoxysilane, γ-(meth)acryloxypropyltrimethoxysilane, γ-(meth)acryloxypropyl dimethyl ethoxysilane,γ-(meth)acryloxypropyl methyl diethoxysilane and γ-(meth)acryloxypropyltriethoxysilane are particularly preferably used. As a surface modifyingmethod, a method (dry method) comprising mixing a surface modifier or asurface modifier diluted with an organic-solvent-containing aqueoussolution in which an organic solvent and water are uniformly mixed suchas an ethanol aqueous solution with an inorganic filler by a ball mill,V-blender or Henschel mixer and then heat-treating the mixture at 50 to150° C. for several minutes to several hours, a method (wet, slurrymethod) comprising adding an inorganic filler to an organic solvent suchas ethanol, a solution in which an organic solvent and water areuniformly mixed such as an ethanol aqueous solution or water so as toform slurry, adding the above surface modifier, treating the resultingmixture at room temperature to a reflux temperature for several minutesto several hours, removing the solvent by a known method such asdecantation or evaporation and then heat-treating the resulting productat 50 to 150° C. for several hours, and a method (spraying method)comprising spraying a surface modifier or the above aqueous solutiondirectly on a high-temperature inorganic filler can be used. Theinorganic filler should be treated as appropriate by a method taking thecharacteristics of a silane coupling agent and the inorganic filler intoaccount. As a matter of course, a commercial inorganic filler havingalready been surface-modified may be used as it is or may be furthersurface-modified by the above methods or other methods. The aboveethanol aqueous solution may be neutral or acidic. The amount of thesurface modifier is preferably 0.1 to 20 parts by weight, morepreferably 0.1 to 15 parts by weight, particularly preferably 0.1 to 10parts by weight, based on 100 parts by weight of the inorganic filler.

Further, the average particle diameter of the inorganic filler ispreferably 0.01 to 5 μm, more preferably 0.01 to 3 μm, much morepreferably 0.01 to 1 μm, particularly preferably 0.01 to 0.1 μm, toimpart gloss and transparency to a cured surface. To exhibit the aboveadvantage, silica called a hydrophobic aerosil (Nippon Aerosil Co.,Ltd.) such as R972, R972V, R972CF, RX200, RY200, R202, R805, R976, R812or R812S or a hydrophilic aerosil such as OX-50 or 50 can be preferablyused. Since they are commercially available as hydrophobed products ofhigh-purity silicon dioxide aerosol, they are free from need to besurface-treated, and since the average particle diameter is 0.05 μm orsmaller, i.e., the primary particle diameter is smaller than thewavelength of visible light, a cured product containing such silicahardly allows visible light to reflect diffusely and shows goodtransparency. Accordingly, these inorganic fillers can be preferablyused. Of these, R972, R812, R812S and R805 are suitable.

Further, to impart mechanical strength and adjust viscosity, a fillerhaving an average particle diameter of 5 to 100 μm, preferably 5 to 30μm, may also be added in such an amount that does not impair thecharacteristics of the present invention.

The amount of the inorganic filler is selected in consideration of theshape and particle diameter of the inorganic filler, the viscosity ofthe composite material and other factors and is preferably 10 to 900parts by weight, more preferably 10 to 600 parts by weight, much morepreferably 10 to 400 parts by weight, based on 100 parts by weight ofthe polymerizable compound (C).

Further, as in the case of the above transparency, the X-ray contrastproperty of the cured product of the composite material can bedetermined according to an application in which it is used. Based on thesensitivity of an X-ray which is generally used in dentistry, the curedproduct generally shows an Al equivalent of 45% or higher, preferably 55to 400%, more preferably 80 to 300%, when the thickness of the curedproduct of the composite material is 2.0 mm.

Applications of the polymerizable composition of the present invention,the cured product thereof and the composite material containing powderof the cured product are not particularly limited. Illustrative examplesof dental applications include dental composite materials such as asealant, a cavity lining material, adhesive resin cement, a resin filler(composite resin), a hard resin, and artificial teeth. Meanwhile,illustrative examples of industrial applications other than dentalapplications include industrial composite materials such as hard coatmaterials, binders for resins, glass plates for the windows of housesand vehicles in which inorganic glass has conventionally been used,shielding materials required to be ultraviolet-resistant orradiation-resistant, and degradation preventing materials for resins andthe like.

Hereinafter, the present invention will be further described by use ofExamples and Comparative Examples. The present invention shall not belimited by these Examples. The light transmittance (%) in Examples wasmeasured by measuring a cured product having a thickness of 2.0 mm byuse of a spectrophotometer (UV-160A, product of Shimadzu Corporation) ata visible light wavelength of 560 nm. To measure the X-ray contrastproperty (in accordance with the method described in 5.11 of JIST6514-1993), a circular cured product having a thickness of 2.0 mm wasX-ray photographed by X-ray control equipment (PCX-100, product of AsahiRoentgen Ind. Co., Ltd.) and then an Al equivalent (%) was calculated onthe basis of the density (100%) of an image of an Al plate having thesame thickness by a densitometer (PDA15, product of Konica MinoltaHoldings, Inc.). The compressive strength was measured by immersing acylindrical cured product with a diameter of 3 mm and a thickness of 3mm which had been irradiated with light by visible light irradiationequipment (α-Light, product of Morita Corporation) for 3 minutes, inwater (37° C.) for 24 hours and then measuring the resulting curedproduct by use of an autograph (AGS-2000G, product of ShimadzuCorporation) at a crosshead speed of 2.0 mm/min.

EXAMPLE 1

100 parts by weight of water-dispersed zirconia sol (product of CHEMATCO., LTD., zirconia: 20 wt %, acetic acid: 15 wt %, water: 65 wt %,zirconia particle diameter: 5 to 10 nm), 400 parts by weight of methanol(hereinafter abbreviated as “MeOH”) and 20 parts by weight ofγ-methacryloxypropyl trimethoxysilane (hereinafter abbreviated as“γ-MPTS”) were charged into an eggplant-shaped flask and stirred at roomtemperature for 48 hours. Then, 45 parts by weight of trimethylolpropanetrimethacrylate (hereinafter abbreviated as “TMPT”) was added andstirred for several minutes, and the solvent was then removed for anamount of 250 parts by weight by a rotary evaporator under reducedpressure at 40° C. Isopropyl alcohol (hereinafter abbreviated as “IPA”)was added in the same amount as that of the removed solvent, and theresulting mixture was concentrated by a rotary evaporator under reducedpressure at 60° C. until most of the solvent was removed. Then, theresulting product was dried under reduced pressure by a dryer at atemperature of 80° C. for 6 hours to replace the solvent by TMPT whichwas a polymerizable compound so as to obtain 85 parts by weight oftransparent polymerizable composition (zirconia concentration: 20 wt %).

To 100 parts by weight of the polymerizable composition, 0.3 parts byweight of benzoyl peroxide (hereinafter abbreviated as “BPO”) was addedas a polymerization initiator. After the resulting mixture was filled ina mold having a thickness of 2.0 mm, heat polymerization was carried outin a heating compression molding machine at a pressure of 0.5 MPa and120° C. for 10 minutes. The obtained cured product of the transparentcomposite composition was evaluated with respect to light transmittance(%) at a visible light wavelength of 560 nm and an X-ray contrastproperty in terms of Al equivalent (%) (Table 1).

EXAMPLE 2

A polymerizable composition (zirconia concentration: 26 wt %) wasprepared in the same manner as in Example 1 except that the amount ofTMPT was changed to 22 parts by weight, and the light transmittance andX-ray contrast property of the cured product thereof were evaluated(Table 1).

EXAMPLE 3

A polymerizable composition (zirconia concentration: 30 wt %) wasprepared in the same manner as in Example 1 except that the amount ofTMPT was changed to 11.5 parts by weight, and the light transmittanceand X-ray contrast property of the cured product thereof were evaluated(Table 1).

EXAMPLE 4

A polymerizable composition (zirconia concentration: 30 wt %) wasprepared in the same manner as in Example 3 except that thepolymerizable compound was a uniform mixture comprisingditrimethylolpropane tetramethacrylate (hereinafter abbreviated as“D-TMP”) represented by the above formula (IV) and HX-220 (product ofNippon Kayaku Co., Ltd.) which was a polyester acrylate based compoundrepresented by the above formula (V) in a molar ratio of D-TMP/HX-220 of½, and the light transmittance and X-ray contrast property of the curedproduct thereof were evaluated (Table 1).

EXAMPLE 5

To a separable flask, 100 parts by weight of MeOH-dispersed titania sol(product of CATALYSTS & CHEMICALS IND. CO., LTD., titania coated withsilica-zirconia: 30 wt %, MeOH: 70 wt %, titania particle diameter: 8 to11 nm) and 100 parts by weight of MeOH were added and stirred forseveral minutes until a uniform mixture was obtained. To the mixture,121.8 parts by weight of uniform hydrolyzed solution prepared by adding76 parts by weight of γ-methacryloxypropylmethyl dimethoxysilane to 46parts by weight of 0.1 wt % acetic-acid aqueous solution and stirringthe mixture at room temperature for 1 hour for hydrolysis was added, andthe resulting mixture was stirred in an oil bath of 90° C. for severalminutes. Then, as 100 parts by weight of MeOH was gradually removed, 14parts by weight of TMPT was added dropwise. After the resulting mixturewas cooled to room temperature, 400 parts by weight of IPA was added,the solvent was removed by a rotary evaporator under reduced pressure at40° C., the resulting product was dried under reduced pressure by adryer at a temperature of 80° C. for 6 hours to completely replace thesolvent with TMPT so as to obtain 120 parts by weight of transparentpolymerizable composition (titania concentration: 25 wt %).

To 120 parts by weight of the polymerizable composition, 0.3 parts byweight of BPO was added as a polymerization initiator, and the curedproduct of the composite composition was obtained in the same manner asin Example 1. The light transmittance and X-ray contrast property of theobtained transparent cured product were evaluated (Table 1).

EXAMPLE 6

A polymerizable composition (titania concentration: 35 wt %) wasprepared in the same manner as in Example 5 except that 26 parts byweight of 0.1 wt % acetic acid aqueous solution, 43 parts by weight ofγ-methacryloxypropylmethyl dimethoxysilane and 13 parts by weight ofTMPT were used, and the light transmittance and X-ray contrast propertyof the cured product thereof were evaluated (Table 1).

EXAMPLE 7

A polymerizable composition (titania concentration: 38 wt %) wasprepared in the same manner as in Example 5 except that 26 parts byweight of 0.1 wt % acetic acid aqueous solution, 43 parts by weight ofγ-methacryloxypropylmethyl dimethoxysilane and 6 parts by weight of TMPTwere used, and the light transmittance and X-ray contrast property ofthe cured product thereof were evaluated (Table 1).

COMPARATIVE EXAMPLE 1

100 parts by weight of zirconia powder (prototype of Nippon Aerosil Co.,Ltd.) having a primary particle diameter of 20 nm was added to a mixedsolvent comprising 1,000 parts by weight of ethanol (hereafterabbreviated as “EtOH”), 5 parts by weight of γ-MPTS and 1 part by weightof distilled water and refluxed for 2 hours. Then, EtOH was removed by arotary evaporator, and the resulting product was then dried underreduced pressure by a dryer at 80° C. in a nitrogen atmosphere for 10hours. After 30 parts by weight of the modified zirconia powder wasadded to 100 parts by weight of TMPT and 0.3 parts by weight of BPO wasadded, a cured product was prepared in the same manner as in Example 1.It was a white cured product without transparency. The lighttransmittance and X-ray contrast property of the cured product wereevaluated (Table 1).

COMPARATIVE EXAMPLE 2

100 parts by weight of water-dispersed zirconia sol (zirconia: 20 wt %,acetic acid: 15 wt %, distilled water: 65 wt %, zirconia particlediameter: 5 to 10 nm) and 400 parts by weight of MeOH were charged intoan eggplant-shaped flask and stirred at room temperature for 48 hours.Then, 32 parts by weight of TMPT was added and stirred for severalminutes, and the solvent was removed by a rotary evaporator underreduced pressure at 40° C. IPA was added in the same amount as 300 partsby weight of the removed solvent, and the resulting mixture wasconcentrated to completely replace the solvent by TMPT so as to obtain67 parts by weight of white composite composition (zirconiaconcentration: 30 wt %) having no transparency.

To 67 parts by weight of the composite composition, 0.3 parts by weightof BPO was added as a polymerization initiator. After the resultingmixture was filled in a mold having a thickness of 2.0 mm, heatpolymerization was carried out in a heating compression molding machineat a pressure of 0.5 MPa and 120° C. for 10 minutes. The lighttransmittance and X-ray contrast property of the obtained white curedproduct were evaluated (Table 1).

EXAMPLE 8

A polymerizable composition (titania concentration: 25 wt %) wasprepared in the same manner as in Example 5 except that thepolymerizable compound was a uniform mixture comprising 75 wt % ofdi(methacryloxyethyl)trimethylhexamethylene diurethane (hereinafterabbreviated as “UDMA”) and 25 wt % of triethylene glycol dimethacrylate(hereinafter abbreviated as “3G”). The light transmittance and X-raycontrast property of the cured product thereof were evaluated (Table 1).Further, compressive strength was also measured and found to be 440 MPa.

COMPARATIVE EXAMPLE 3

To 100 parts by weight of polymerizable compound obtained by mixing 75wt % of UDMA and 25 wt % of 3G, 0.3 parts by weight of camphorquinone,0.06 parts by weight of 2-n-butoxyethyl p-N,N-dimethylaminobenzoate and0.084 parts by weight of 2,6-di-t-butyl-p-cresol were added to prepare aphotopolymerizable compound. After 25 parts by weight of titania powder(T-805, product of Nippon Aerosil Co., Ltd.) having a primary particlediameter of 21 nm was added to 100 parts by weight of thephotopolymerizable compound, the resulting mixture was irradiated withlight by use of visible light irradiation equipment α-light (product ofMorita Corporation) for 3 minutes to give a circular cured producthaving a thickness of 2.0 mm. It was a white cured product having notransparency. The light transmittance and X-ray contrast property of thecured product were evaluated (Table 1). Further, although preparation ofa test piece for measurement of compressive strength was attempted, thesurface opposite to a surface exposed to light was not fully cured,thereby making it impossible to measure the compressive strength (it wasnot cured to 3.0 mm which was the thickness of the test piece). TABLE 1Solid Light Al Concentration Transmittance Equivalent Ex. No. (wt %) (%)(%) Ex. 1 20 73.4 161 Ex. 2 26 66.2 223 Ex. 3 30 71.0 264 Ex. 4 30 70.5280 Ex. 5 25 18.7 61 Ex. 6 35 17.8 72 Ex. 7 38 13.6 86 Ex. 8 25 37.6 56C. Ex. 1 30 0.3 211 C. Ex. 2 30 0.3 256 C. Ex. 3 25 0.3 46Ex.: Example,C. Ex.: Comparative Example

EXAMPLE 9

A pass product obtained by milling the cured product obtained in Example3 by a ball mill and sieving the resulting powder by a sieve having anopening of 53 μm was collected. After the product was washed withdistilled water and EtOH, it was dried under reduced pressure by a dryerat a temperature of 80° C. for 2 hours (average particle diameter: 29μm, hereinafter abbreviated as “T/Zr-1”). Then, to 100 parts by weightof polymerizable compound obtained by uniformly mixing 15 wt % of 3G, 25wt % of 1,3-bis(methacryloxyethoxy)benzene (hereinafter abbreviated as“RDMA”) and 60 wt % of 2,2-bis[4-(methacryloxyethoxy)phenyl]propane(hereinafter abbreviated as “2.6E”), 0.3 parts by weight ofcamphorquinone, 0.06 parts by weight of 2-n-butoxyethylp-N,N-dimethylaminobenzoate and 0.084 parts by weight of2,6-di-t-butyl-p-cresol were added to prepare a photopolymerizablecompound.

To 100 parts by weight of the photopolymerizable compound, 42 parts byweight of T/Zr-1 and 18 parts by weight of R972 (product of NipponAerosil Co., Ltd.) which was hydrophobic colloidal silica were added toobtain a photopolymerizable compound. This was irradiated with light byuse of visible light irradiation equipment α-light (product of MoritaCorporation) for 3 minutes to obtain a transparent cured product of thecomposite material. The light transmittance, X-ray contrast property andcompressive strength of the cured product were evaluated (Table 2).

EXAMPLE 10

A pass product obtained by milling the cured product obtained in Example4 by a ball mill and sieving the resulting powder by a sieve having anopening of 53 μm was collected. After the product was washed withdistilled water and EtOH, it was dried under reduced pressure by a dryerat a temperature of 80° C. for 2 hours (average particle diameter: 26μm, hereinafter abbreviated as “D/Zr-2”). Then, to 100 parts by weightof the same photopolymerizable compound as used in Example 9, 42 partsby weight of D/Zr-2 and 18 parts by weight of R972 were added, and atransparent cured product of the composite material was obtained in thesame manner as in Example 9. The light transmittance, X-ray contrastproperty and compressive strength of the cured product were evaluated(Table 2).

COMPARATIVE EXAMPLE 4

A pass product obtained by milling the cured product obtained inComparative Example 1 by a ball mill and sieving the resulting powder bya sieve having an opening of 53 μm was collected (average particlediameter: 27 μm, hereinafter abbreviated as “Zr-3”). Then, to 100 partsby weight of the same photopolymerizable compound as used in Example 9,42 parts by weight of Zr-3 and 18 parts by weight of R972 were added,and a cured product was prepared in the same manner as in Example 9. Thecured product had no transparency. The light transmittance, X-raycontrast property and compressive strength of the cured product wereevaluated (Table 2).

COMPARATIVE EXAMPLE 5

A pass product obtained by milling the cured product obtained inComparative Example 2 by a ball mill and sieving the resulting powder bya sieve having an opening of 53 μm was collected (average particlediameter: 28 μm, hereinafter abbreviated as “Zr-4”). Then, to 100 partsby weight of the same photopolymerizable compound as used in Example 9,42 parts by weight of Zr-4 and 18 parts by weight of R972 were added,and a cured product was prepared in the same manner as in Example 9. Thecured product had no transparency. The light transmittance, X-raycontrast property and compressive strength of the cured product wereevaluated (Table 2).

COMPARATIVE EXAMPLE 6

44.4 parts by weight of R972 and 0.5 parts by weight of BPO were addedto 100 parts by weight of polymerizable compound comprising 90 wt % ofTMPT and 10 wt % of UDMA, and heat polymerization was carried out by aheating compression molding machine at a pressure of 0.5 MPa and 120° C.for 10 minutes. A pass product obtained by milling the obtained curedproduct by a ball mill and sieving the resulting powder by a sievehaving an opening of 53 μm was collected (average particle diameter: 23μm, hereinafter abbreviated as “T-90f”). Then, to 100 parts by weight ofthe same photopolymerizable compound as used in Example 9, 42 parts byweight of T-90f and 18 parts by weight of R972 were added, and a curedproduct was prepared in the same manner as in Example 9. The lighttransmittance, X-ray contrast property and compressive strength of thecured product were evaluated (Table 2). TABLE 2 Light Al CompressiveTransmittance Equivalent Strength Ex. No. (%) (%) (MPa) Ex. 9 4.0 128434 Ex. 10 4.5 135 485 C. Ex. 4 0.3 99 — C. Ex. 5 0.3 112 — C. Ex. 6 1.038 323Ex.: Example,C. Ex.: Comparative Example

EXAMPLE 11

58.2 wt % of T/Zr-1 obtained in Example 9, 40 wt % of surface-treatedGM8235 and 1.8 wt % of sodium salt of N-phenyl glycine were mixedtogether by a ball mill to form uniform powdery material.

39 wt % of 2-hydroxyethyl methacrylate, 15 wt % of epoxy resin (VR-90,product of Showa Polymer Co., Ltd.), 15 wt % of 2.6E, 10 wt % of 3G, 16wt % of 4-methacryloxytrimellitic anhydride, 4 wt % of4-methacryloxytrimellitic acid, 1 wt % of benzoylperoxide, 0.06 wt % of2,6-di-t-butylresorcin and 0.03 wt % of 4-methoxyphenol were mixedtogether to form a uniform monomer mixture.

After the powdery material and the monomer mixture were placed in amortar in the same amount and kneaded uniformly, the mixture wasimmediately filled in the same mold for measurements of lighttransmittance and an X-ray contrast property as used in Example 9.

The obtained cured product showed a light transmittance at a visiblelight wavelength of 560 nm of 50% and an X-ray contrast property interms of Al equivalent of 150%. Thus, it had suitable properties as adental cement material having transparency and an excellent X-raycontrast property.

The surface-treated GM8235 was prepared in the following manner.

316 ml of ethanol, 100 g of γ-methacryloxypropyl trimethoxysilane and 20g of purified water were added to a separable flask at room temperatureto prepare a uniform solution. While this solution was agitated, 1 kg ofbarium glass (average particle diameter: 1 am, product of Shot Co.,Ltd., GM8235) was gradually added to prepare slurry. Then, after thisslurry was refluxed under heating for 2 hours, the solvent was removedby an evaporator. The obtained powder was heated in a nitrogenatmosphere at 80° C. for 48 hours to obtain surface-treated GM8235.

EXAMPLE 12

100 parts by weight of the same water-dispersed zirconia sol as used inExample 1, 400 parts by weight of MeOH and 20 parts by weight of Y-MPTSwere charged into an eggplant-shaped flask and stirred at roomtemperature for 48 hours. Then, after 11.5 parts by weight of TMPT wasadded and stirred for several minutes, the solvent was removed for anamount of 250 parts by weight by a rotary evaporator under reducedpressure at 40° C. To the content of the flask, a solution prepared bydissolving 0.3 parts by weight of BPO in 250 parts by weight of IPA wasadded. After concentrated again by a rotary evaporator until most of thesolvent was removed, the content of the flask was transferred onto atray and dried under reduced pressure at a temperature of 60° C. for 6hours to replace the solvent by TMPT which was a polymerizable compoundso as to obtain 52 parts by weight of transparent polymerizablecomposition (zirconia concentration: 30 wt %).

After this polymerizable composition was filled in a mold having athickness of 2.0 mm, heat polymerization was carried out by a heatingcompression molding machine at a pressure of 0.5 MPa and 120° C. for 20minutes. As a result, the obtained transparent cured product of thecomposite composition showed a light transmittance at a visible lightwavelength (560 nm) of 71.4% and an X-ray contrast property in terms ofAl equivalent of 281%.

EXAMPLE 13

A pass product obtained by milling the cured product obtained in Example12 by a ball mill and sieving the resulting powder by a sieve having anopening of 53 μm was collected. After the product was washed withdistilled water and EtOH, it was dried under reduced pressure at atemperature of 80° C. for 2 hours (average particle diameter: 25 μm,hereinafter abbreviated as “D/Zr-3”). Then, to 100 parts by weight ofthe same photopolymerizable compound as used in Example 9, 42 parts byweight of D/Zr-3 and 18 parts by weight of R972 were added, and atransparent cured product of the composite material was obtained in thesame manner as in Example 9. As a result, the cured product showed alight transmittance of 4.3%, an X-ray contrast property in terms of Alequivalent of 133% and a compressive strength of 453 MPa.

EFFECT OF INVENTION

According to the present invention, there are obtained a polymerizablecomposition having excellent transparency and an X-ray contrastproperty, a cured product obtained by polymerizing the composition, anda composite material comprising powder of the cured product. They can beapplied to a wider range of dental materials as well as to a wide rangeof industrial applications other than dental materials.

1. A polymerizable composition comprising: (A) an inorganic oxide havingan X-ray contrast property and an average particle diameter of 100 nm orsmaller, (B) a surface modifier, and (C) a polymerizable compound. 2.The polymerizable composition of claim 1, further comprising (D) apolymerization initiator.
 3. The polymerizable composition of claim 1,which is in the form of a polymerizable colloidal solution in which theinorganic oxide (A) is dispersed uniformly.
 4. The polymerizablecomposition of claim 3, prepared by treating a mixture of an aqueouscolloidal solution of an inorganic oxide having an X-ray contrastproperty and an average particle diameter of 100 nm or smaller in anaqueous organic solvent and the surface modifier (B) with thepolymerizable compound (C) to replace the aqueous organic solvent andwater in the mixture with the polymerizable compound (C).
 5. Thepolymerizable composition of claim 1, further comprising (E) a colloidstabilizer.
 6. The polymerizable composition of claim 5, wherein thecolloid stabilizer (E) is acetic acid.
 7. The polymerizable compositionof claim 1, wherein the inorganic oxide (A) comprises ZrO₂ and/or TiO₂as a main constituent(s).
 8. The polymerizable composition of claim 1,wherein the average particle diameter of the inorganic oxide (A) is 1 to100 nm.
 9. The polymerizable composition of claim 1, wherein the contentof the surface modifier (B) is 10 to 500 parts by weight based on 100parts by weight of the inorganic oxide (A), and the content of thepolymerizable compound (C) is 10 to 1,000 parts by weight based on 100parts by weight of the inorganic oxide (A).
 10. The polymerizablecomposition of claim 2, wherein the content of the polymerizationinitiator (D) is 0.01 to 5 parts by weight based on 100 parts by weightof the total of the components (A), (B) and (C).
 11. The polymerizablecomposition of claim 5, wherein the content of the colloid stabilizer(E) is 0.1 to 150 parts by weight based on 100 parts by weight of thecomponent (A).
 12. The polymerizable composition of claim 1, wherein thesurface modifier (B) is an alkoxysilane compound.
 13. The polymerizablecomposition of claim 1, wherein the surface modifier (B) is at least onecompound selected from the group consisting of compounds represented bythe following formula (I):SiR¹ _(a)R² _(b)(OR³)_(c)  (I) wherein R¹ and R² each independentlyrepresent a substituent with 1 to 20 carbon atoms which may have anether bond, an ester bond, an epoxy bond or a carbon-carbon double bondand which may also have a nitrogen atom, a sulfur atom or a phosphorusatom, R³ represents a hydrogen atom or a substituent with 1 to 20 carbonatoms which may have an ether bond, an ester bond or a carbon-carbondouble bond and which may also have a nitrogen atom, a sulfur atom or aphosphorus atom, a and b represent an integer of 0 to 3, and c satisfiesc=4−a−b and represents an integer of 1 to
 4. 14. The polymerizablecomposition of claim 13, wherein the surface modifier (B) is a compoundresulting from hydrolyzation or partial hydrolyzation of at least onecompound represented by the formula (I) or condensation of two or moremolecules of the compound.
 15. The polymerizable composition of claim 2,whose cured product having a thickness of 2.0 mm shows a lighttransmittance at a visible light wavelength of 560 nm of 1% or higherand an X-ray contrast property in terms of Al equivalent of 45% orhigher.
 16. A cured product of the polymerizable composition of claim 15or powder of the cured product.
 17. The powder of claim 16, having anaverage particle diameter of 1 to 100 μm.
 18. A composite materialcomprising the powder of claim
 16. 19. A composite material comprising:(C) a polymerizable compound, (D) a polymerization initiator, and (F)the powder of claim
 16. 20. A dental composite material comprising thepowder of claim
 16. 21. A dental composite material comprising: (C) apolymerizable compound, (D) a polymerization initiator, and (F) thepowder of claim
 16. 22. The material of claim 21, whose cured producthaving a thickness of 2.0 mm shows a light transmittance at a visiblelight wavelength of 560 nm of 1% or higher and an X-ray contrastproperty in terms of Al equivalent of 45% or higher.
 23. Thepolymerizable composition of claim 1, wherein the polymerizable compound(C) is at least one compound selected from the group consisting ofmonofunctional, bifunctional and polyfunctional (meth)acrylates,urethane compounds and polyester di(meth)acrylate compounds.